The present invention relates to a brake booster for vehicles, particularly automotive vehicles.
The present inventor first presented the following invention of a brake booster system in Japanese Patent Application No. 58-186498, filed on Oct. 5, 1983.
Referring to FIG. 1, this brake booster system will be briefly described hereinafter. The system comprises a sensor 1 sensing the depression force applied to a brake pedal 2 by an operator and outputting a corresponding depression force signal (a), a sensor 3 directly or indirectly sensing the rate of deceleration of the a vehicle due to braking, and outputting a corresponding actual deceleration signal (b), a booster 5 arranged between the brake pedal 2 and a master brake cylinder 4 and including a reference fluid pressure chamber 5a connected to atmosphere and a working fluid pressure chamber 5b both defined within a power cylinder 5c by a movable wall 5d having a peripheral, flexible diaphragm 5e, a fluid pressure source 6 communicating with the working pressure chamber 5b, an electromechanical valve 7 provided intermediate a conduit 8 communicating the working fluid pressure chamber 5b to the fluid pressure source 6 or to atmosphere and actuated by means of a valve-control signal (c) so as to match the actual deceleration to a target deceleration value, a function generator 9 outputting a target deceleration signal (d) in accordance with the depression force signal (a), and a comparator 10 receiving the target deceleration signal (d) and the actual deceleration and outputting the valve-control signal (c).
The brake booster system operates as follows: The foot of the operator applies a force to the brake pedal 2. Thus, the function generator 9 outputs a corresponding target deceleration signal (d) depending on a depression force signal (a) from the depression force sensor 1 and at the same time the deceleration sensor 3 outputs a corresponding actual deceleration signal (b). The comparator 10 receives the target deceleration signal (d) and the actual deceleration signal (b) and outputs a corresponding valve-control signal (c). The electro-mechanical valve 7 is actuated by means of the valve-control signal (c), thus supplying a suitable fluid pressure from the fluid pressure source 6 or from atmosphere to the working pressure chamber 5b.
Thus, a desired braking force is achieved. In accordance with the above-described brake booster system, equal brake pedal depression forces can effect equal target decelerations, even if the weights of vehicles having the above-described brake booster system may differ.
Since the brake booster system of FIG. 1 which uses a fluid pressure source 6 other than the vacuum from the intake manifold supplies a desired fluid pressure to the working fluid pressure chamber side of the movable wall 5d by way of the electro-mechanical valve 7, the booster 5 can employ a structure in which the fluid pressure chambers 5a and 5b are separated by the movable wall 5d without providing a booster valve arrangement between the fluid pressure chambers 5a and 5b and can obviate a well-known vacuum-type booster structure. Thus, in the novel system when the part of the system supplying fluid pressure from the fluid pressure source 6 to the working fluid pressure chamber 5b encounters any difficulty, the booster 5 may malfunction or become altogether inoperative, so that the desired or any braking force at all may not be achieved.